Add test and fix last commit

Author: mrdaybird

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -13004,20 +13004,19 @@ ScalarEvolution::howManyLessThans(const SCEV *LHS, const SCEV *RHS,
              *BECountIfBackedgeTaken = nullptr;
   if (!isLoopInvariant(RHS, L)) {
     const auto *RHSAddRec = dyn_cast<SCEVAddRecExpr>(RHS);
-    bool RHSNoWrap = RHSAddRec->getNoWrapFlags();
-    if (RHSAddRec != nullptr && RHSAddRec->getLoop() == L && RHSNoWrap) {
+    if (PositiveStride && RHSAddRec != nullptr && RHSAddRec->getLoop() == L &&
+        RHSAddRec->getNoWrapFlags()) {
       // The structure of loop we are trying to calculate backedge count of:
       //
       //  left = left_start
       //  right = right_start
       //
       //  while(left < right){
       //    ... do something here ...
-      //    left += s1; // stride of left is s1>0
-      //    right -= s2; // stride of right is -s2 (s2 > 0)
+      //    left += s1; // stride of left is s1 (s1 > 0)
+      //    right += s2; // stride of right is s2 (s2 < 0)
       //  }
       //
-      // Here, left and right are converging somewhere in the middle.
 
       const SCEV *RHSStart = RHSAddRec->getStart();
       const SCEV *RHSStride = RHSAddRec->getStepRecurrence(*this);
@@ -13028,7 +13027,6 @@ ScalarEvolution::howManyLessThans(const SCEV *LHS, const SCEV *RHS,
       //    Where, End = max(RHSStart, Start)
 
       // Check if RHSStride < 0 and Stride - RHSStride will not overflow.
-      // FIXME: Can RHSStride be positive?
       if (isKnownNegative(RHSStride) &&
           willNotOverflow(Instruction::Sub, /*Signed=*/true, Stride,
                           RHSStride)) {

llvm/test/Analysis/ScalarEvolution/pr92560.ll

@@ -102,4 +102,35 @@ while.end:
   ret void
 }
 
+; abs(left_stride) != abs(right_stride)
+define dso_local void @simple2() local_unnamed_addr {
+; CHECK-LABEL: 'simple2'
+; CHECK-NEXT:  Classifying expressions for: @simple2
+; CHECK-NEXT:    %right.08 = phi i32 [ 50, %entry ], [ %add2, %while.body ]
+; CHECK-NEXT:    --> {50,+,-5}<nsw><%while.body> U: [25,51) S: [25,51) Exits: 25 LoopDispositions: { %while.body: Computable }
+; CHECK-NEXT:    %left.07 = phi i32 [ 0, %entry ], [ %add, %while.body ]
+; CHECK-NEXT:    --> {0,+,4}<nuw><nsw><%while.body> U: [0,21) S: [0,21) Exits: 20 LoopDispositions: { %while.body: Computable }
+; CHECK-NEXT:    %add = add nuw nsw i32 %left.07, 4
+; CHECK-NEXT:    --> {4,+,4}<nuw><nsw><%while.body> U: [4,25) S: [4,25) Exits: 24 LoopDispositions: { %while.body: Computable }
+; CHECK-NEXT:    %add2 = add nsw i32 %right.08, -5
+; CHECK-NEXT:    --> {45,+,-5}<nsw><%while.body> U: [20,46) S: [20,46) Exits: 20 LoopDispositions: { %while.body: Computable }
+; CHECK-NEXT:  Determining loop execution counts for: @simple2
+; CHECK-NEXT:  Loop %while.body: backedge-taken count is i32 5
+; CHECK-NEXT:  Loop %while.body: constant max backedge-taken count is i32 5
+; CHECK-NEXT:  Loop %while.body: symbolic max backedge-taken count is i32 5
+; CHECK-NEXT:  Loop %while.body: Trip multiple is 6
+;
+entry:
+  br label %while.body
 
+while.body:
+  %right.08 = phi i32 [ 50, %entry ], [ %add2, %while.body ]
+  %left.07 = phi i32 [ 0, %entry ], [ %add, %while.body ]
+  %add = add nuw nsw i32 %left.07, 4
+  %add2 = add nsw i32 %right.08, -5
+  %cmp = icmp slt i32 %add, %add2
+  br i1 %cmp, label %while.body, label %while.end
+
+while.end:
+  ret void
+}